InterviewBit Problems   Postorder Traversal : Unsolved

About the Postorder Traversal : Unsolved category (1)
Easiest Approach EXPLAINED : Stack Based Solution (3)
I can't seem to figure out what the problem is (1)
Did the question but at the cost of destruction of the entire tree, any suggestion (1)
What's wrong in following code? (1)
Solution Template Erratic (1)
Why is this giving runtime error for some inputs? (1)
What's the right format of the input? (2)
Unable to detect problem in approach (1)